1. Field of the Invention
The present invention relates to an input device, and more particularly, to an input device which is suitable for a small portable terminal or the like having a plurality of input keys.
2. Description of the Related Art
Generally, an input device having a plurality of input keys has been widely used in numerical keypads such as keyboard of a personal computer, electronic calculator, mobile phone or the like. Even though there are various types of input devices having different inputting modes, input devices that rely on the changes in electrostatic capacitance can be used due to the capability of reducing the size and cost as compared to the other types of input devices.
The input device that relies on the changes in electrostatic capacitance is composed of input keys printed on a top sheet, flat electrodes disposed in a position facing the input keys, and a controller for detecting the change in electrostatic capacitance of the electrodes. In addition, if the controller detects the change in electrostatic capacitance of the electrodes generated when an operator approaches or touches the input keys, the input device can input desired keys.
However, in the input device that relies on the change in electrostatic capacitance, since the input keys face the electrodes, and thus the number of the input keys is equal to that of the electrodes, the increase in the number of the input keys will cause the following three setbacks.
The first problem is the forming of the electrodes and the conductive wires. If the number of the input keys increases, the number of the conductive wires connected to the electrodes also increases by the increased number of the electrodes as well as the electrodes facing the input keys. Accordingly, if the increased number of input keys are formed on a substrate having the same area as the existing substrate, the electrodes and conductive wires are be formed smaller so as to fit in the area. In addition, as the area of the substrate becomes smaller, the electrodes are decreased in size and the conductive wires are made thin. Thus, this problem makes it difficult to form the input device.
The second problem is the reduction in size of the substrate. When the number of the input keys increases, if electrodes having the same area as the existing electrodes and conductive wires are formed, the substrate on which the electrodes and the conductive wires are formed is enlarged. Thus, this problem makes it difficult to make the input device slim.
The third problem is the increase in manufacturing cost, which results from the first problem. As described in the first problem, it is very difficult to form the electrodes and the conductive wires when the number of the input keys increases unless the substrate is enlarged. That is, a sophisticated technique is required to form small electrodes and thin conductive wires, thus consequentially increasing the manufacturing cost of the input device. In other words, the smaller the area of the substrate becomes, the higher the cost of manufacturing becomes.